The problem with thixotropic paints and lacquers based on polyamide-modified alkyd resins (see e.g. U.S. Pat. No. 2,663,649) is that the components additionally present in the lacquer, particularly hydroxyl group-containing solvents such as, for example, alcohols, glycols and some organic paint pigments (e.g. phthalocyanine blue, Hansa yellow and Bordeaux red), have a negative effect on the thixotropy. However, SiO.sub.2 -flatting agents also have a similar effect.
Immediately after being produced, fine-particled SiO.sub.2 -flatting agents can be easily de-agglomerated into individual particles with the application of low shearing forces when incorporated into lacquer. This behaviour is desirable because remaining agglomerates lead to clearly visible specks in the applied lacquer film. However, if fine-particled SiO.sub.2 -flatting agents are subjected to a pressure, more solid agglomeration can result. This effect is increased if the pressure is exerted over a lengthy period of time. This can cause the good dispersibility of a product which initially has excellent dispersibility, to deteriorate during storage because of stress such as can occur during storage and transportation, whereupon said product is judged unacceptable by the user.
In thixotropic paints and lacquers, because of their gel-like properties, no sedimentation of flatting agents or pigment particles is observed. The particles remain in their position and cannot form a hard, non-dispersible sediment during storage. Exposure to shearing forces causes the viscosity of the system to fall substantially and the particles begin to settle. The particular feature of a thixotropic paint is that the viscosity is very rapidly restored as soon as the mechanical stress ceases. After a short time the paint once again has its original gel-like consistency, which prevents a further settling of the particles.
In a non-thixotropic paint, however, the situation is completely different, because here the SiO.sub.2 -flatting agent particles settle and form a hard sediment. It is very difficult, and in many cases impossible, to re-disperse this sediment into the individual particles again with the equipment common in the paint and lacquer industry.
The formation of a hard sediment can be prevented by coating the flatting agent particles with wax. DE-PS 1 006 100 and DE-AS 1 592 865 describe how the SiO.sub.2 -flatting agent particles can be coated with wax and which waxes can be used.